1. Field of the Invention
The present invention relates generally to inkjet heads for discharging ink onto a recording medium.
2. Description of Related Art
A known inkjet head, such as the inkjet head described in Japanese Patent Application Publication No. JP-A-2005-169839, includes a head main body for discharging the ink, a head control portion for controlling the head main body, and an upper and a lower cover for protecting the head control portion from ink splash. In the known inkjet head, the head main body includes a flow passage unit having a plurality of individual ink flow passages leading to a nozzle, and an actuator unit for changing the volume of individual ink flow passages. The head control portion includes a main board, a plurality of sub-boards electrically connected to the main board and arranged to sandwich the main board, and a driver integrated circuit (“IC”) which includes a heat sink secured to the surface of the sub-boards opposed to the main board. The sub-boards and the driver IC are electrically connected to a flexible printed circuit (“FPC”) with one end electrically connected to the actuator unit. The FPC conveys a signal outputted from the main board via the sub-boards to the driver IC, and conveys a drive signal outputted from the driver IC to the actuator unit. The actuator unit receives the drive signal, and changes the volume of some of the individual ink flow passages and applies pressure to the ink within the individual ink flow passages. In this manner, the ink is discharged from the nozzle, such that a desired image is formed on the paper.
Nevertheless, in the known inkjet head, because the heat sink is covered with an upper cover, the heat generated by the driver IC and the heat sink is captured within the cover. Consequently, the temperature and humidity of space within the inkjet head surrounded by the upper and lower covers increases. Moreover, an external stress is applied on the junction between the connector of the FPC and the electronic parts, and whisker may grow in the connector or the junction of the FPC. Particularly, if the joint member includes a tin based material which does not include lead, the whisker may grow. In addition, the FPC has a narrower pitch with higher wiring density and shorter terminal distance, along with the higher density of the actuator unit, whereby there is a risk that the electrical short circuit occurs due to whisker. A known method for suppressing whisker involves coating gold or adding silver, which increases costs. Further, because the ink temperature within the head main body rises, the ink discharge characteristics vary.